1. Field of the Invention
The present invention relates to a vibrational angular rate sensor, and more specifically to an angular rate sensor of small vibration energy loss or of high quality factor Q, where quality factor Q is 2.pi..times.(energy stored in a vibrational system/energy dissipated per peroid).
2. Description of the Prior Art
Vibrational angular rate sensors are disclosed, for instance in Japanese Unexamined Published (Kokai) Utility Model Applications No. 60-35212 (referred to first prior art sensor), No. 60-41815 (referred to second prior-art sensor, No. 59-25414 (referred to third prior-art sensor), etc. In these prior-art vibrational sensors, a vibrator is supported at vibration nodes by vibrator node-supporting members formed different from the vibrator itself. For instance, in the first prior art sensor, the vibrator node-supporting members are composed of elastic tubes fitted to holes formed in the vibrator and support pins inserted into the elastic tubes. In the second prior-art sensor, the vibrator node-supporting members are made of rigid members and fixed to the vibrator at vibration nodes by bonding, soldering, mechanical caulking, etc. In the third prior-art sensor, an external cell member directly fixed to an object to be measured and a vibrator support base are manufactured separately, and the cell member is made of a relatively soft material to absorb external forces applied thereto.
In these prior-art vibrational sensors, however, there exist various problems in that vibration energy loss is inevitably produced between the vibrator and the node supporting members and therefore the quality factor Q therefore is not high. As a result, the sensor sensitivity is low. In addition, since holes or grooves must be formed precisely in the vibrator and the vibrator node-supporting member to accurately support the vibrator relative to the vibrator external supporting member, the machining and assembling processes are complicated and not easy, and further the vibrator reliability is inadequate. Furthermore, it has been difficult to miniaturize the vibrational sensor from the manufacturing standpoint.
On the other hand, in the vibrational angular rate sensors, two pair of piezoelectric elements are attached to four side surfaces of the square pillar shaped vibrator to drive the vibrator and to detect an angular rate (velocity) applied to the vibrator. Each of these four piezoelectric elements is covered with an thin film electrode and connected to an external circuit through a fine wire.
In more detail, with reference to Prior Art FIGS. 1A, 1B and 1C, the vibrator 1 is formed into a square pillar shape having four side surfaces. A pair of driving piezoelectric elements 2A and 2B and a pair of sensing piezoelectric elements 3A and 3B are attached to each side surface of the vibrator 1, separately, as shown. Further, a pair of thin film driving element electrodes 4A and 4B are formed on the driving piezoelectric elements 2A and 2B by vacuum deposition, sputtering, etc., and a pair of thin film detecting element electrodes 5A and 5B are formed on the detecting piezoelectric elements 3A and 3B by the same thin film forming techniques.
Further, four fine node-support pins 6 are attached to the vibrator 1 at its node positions to support the vibrator 1 relative to an external vibrator support base member 7. Further, the driving element electrodes 4A and 4B and the detecting element electrodes 5A and 5B are connected to an external circuit through four fine conductive wires 4AC, 4BC, 5AC and 5BC.
In the above-mentioned prior-art vibrational sensor, although the four fine conductive wires 4AC, 4BC, 5AC and 5BC are arranged near the vibration nodes, it is very difficult to accurately arrange the conductive wires at the node positions. Additionally, since the conductive wires 4AC, 4BC, 5AC, and 5BC have a mass and also are movable, respectively, there exists a problem in that the vibration nodes are dislocated, so that the quality factor Q of the vibrator is lowered. Further, the connection work of the fine conductive wires 4AC, 4BC, 5AC and 5BC is complicated and therefore not easy. Furthermore, it is difficult to minimize the shape of the vibrator because the fine conductive wires must be fixed onto the vibrator.